Michael Connelly's latest book runs over 100,000 words by my estimate. Agatha Christie's novels typically run less than 70,000 words. So the present-day bestseller is half again as long as the bestseller of the early twentieth century.
Lawrence Block, recalling the beginning of his career writing paperback originals in the 1950s, says he learned that 60,000 words is a standard length for a novel. Today some publishers of mysteries require at least 80,000 words from a first-time author.
Why? Do mystery readers have more leisure to read longer books? That seems unlikely. Are stories more complicated, requiring more pages to work through all the twists and turns of the plot? Probably not.
Here's a clue: Connelly's latest is really two novellas and a short story (labelled "Part I," "Part II," and "Part III") packaged as one big book and called a "novel."
Some speculate that the traditional publishing industry needs to charge $30 for a hardback in order to pay all the costs of bringing the book to market, and that readers are willing to pay that much if they get a lot of pages for their money.
If so, Ebooks and print-on-demand paperbacks may be the best vehicle for the traditional mystery novel of 60,000 to 70,000 words because the costs of production and distribution are so much less. The ebook can sell for around $2.99, and the paperback for $10 to $12. The revenue to the writer can be more than with a hardback from a traditional publisher.